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https://issues.apache.org/jira/browse/NUMBERS-167?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17707639#comment-17707639
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Gilles Sadowski commented on NUMBERS-167:
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bq. As for your use case, I can see that it is a benefit to precompute the log
gamma value for repeat calls. However I cannot say how much the performance
gain will be without getting refamiliar with all the code. I think this change
would also be of benefit to a few of the Statistics distributions.
It turns out that the function was used to compute the [Χ^2^
distribution|https://commons.apache.org/proper/commons-statistics/commons-statistics-distribution/javadocs/api-1.0/org/apache/commons/statistics/distribution/ChiSquaredDistribution.html]'s
inverse cumulative probability. The latter currently calls {{inverse
cumulative probability}} in class
[{{GammaDistribution}}|https://commons.apache.org/proper/commons-statistics/commons-statistics-distribution/javadocs/api-1.0/org/apache/commons/statistics/distribution/GammaDistribution.html]
that uses the default implementation in
[{{AbstractContinuousDistribution}}|https://gitbox.apache.org/repos/asf?p=commons-statistics.git;a=blob_plain;f=commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/AbstractContinuousDistribution.java;hb=HEAD].
Doesn't it entail that it is quite likely that is much slower and potentially
less accurate than what is implemented in that other library?
Note: There seems to be an issue with the generated API docs [at this
page|https://commons.apache.org/proper/commons-statistics/commons-statistics-distribution/javadocs/api-1.0/org/apache/commons/statistics/distribution/GammaDistribution.html#inverseCumulativeProbability-double-]
(the [link to the code of
{{inverseCumulativeProbability}}|https://commons.apache.org/proper/commons-statistics/commons-statistics-distribution/javadocs/api-1.0/src-html/org/apache/commons/statistics/distribution/AbstractContinuousDistribution.html#line.129]
returns "Not Found").
> RegularizedGamma.P with precomputed LogGamma value
> --------------------------------------------------
>
> Key: NUMBERS-167
> URL: https://issues.apache.org/jira/browse/NUMBERS-167
> Project: Commons Numbers
> Issue Type: Wish
> Components: gamma
> Reporter: Gilles Sadowski
> Priority: Minor
> Fix For: 1.2
>
> Attachments: pr_106.patch
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> We have
> {code:java}
> double v = RegularizedGamma.P.value(a, x);
> {code}
> where method {{value}} internally calls {{LogGamma.value(a)}}.
> There is a use-case for
> {code:java}
> double logGammaA = LogGamma.value(a);
> double v = RegularizedGamma.P.value(a, x, logGammaA);
> {code}
> for when the user varies {{x}} but not {{a}}.
> Method name TBD: Another overload of {{value}} may be confusing (?).
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